Violin Making Workbook
Blocks are split from spruce with a grain spacing between one and two grain lines per mm. Corner blocks are oriented so that the grain line bisects the block from the rib mitre to the opposite corner of the block. Neck and bottom blocks are oriented with their grain parallel to the longitudinal axis of the instrument.
The first surface to plane flat (and square to the direction of the split) is the mating surface to the mould. The next surface to be planed, in the case of the corner blocks, is the superior or inferior (depending on whether it is an upper or lower block) surface - also a mating surface to the mould, but not glued to it. This surface is planed flat and 90 degrees square to the first surface (and hence, square to the direction of the split as well).
Once these two planes are established, they are used as a reference to flatten the posterior surface of the block. This is the surface that will sit on the flat plate when the blocks are glued to the mould. The bulk of the waste can be removed with slicing cuts from a broad bladed chisel. This surface is end grain, and must be softened slightly with water before it is planed. A skew cut with the plane is the most efficient cut for removing material under these circumstances. Check frequently with a square from both reference sides, and adjust cuts accordingly. Once the surface is close you should have three sides that are at perfect 90 degree angles to each other. Make the final check on the flat plate to insure that there is no wobble to the posterior aspect of the block.
The neck and bottom blocks are treated in the same way. Establish the mating surface to the mould first, then pick one lateral side and justify it to the first surface. Use these two as a reference to square up the posterior surface. With these three surfaces finished, the remaining lateral side can be pared down to fit the mould mortice. There should be a gap no wider than 1 mm on each side between the block and the mould.
I like to number each block on the medial aspect (mould side) to simplify orientation as the work progresses.
Use a chisel to split-off excess material from the distal portions of each block. With a divider set to the proper distance (bottom ___, lower corner ____, upper corner ____, neck ____), strike-off the height of each block on three sides and use these as reference to cut off the waste with a fine toothed saw.
Place riser blocks on a flat plate and put the mould (posterior side down) on top of the riser blocks. Now place the spruce blocks in position in their motices in the mould. Scribe a line across the block's surface where it meets the anterior surface of the mould. Take each block in turn and smear a fairly generous amount of yellow glue below this scribe line. Place each block in it's mortice on the mould and firmly push the surface to be glued against the mould. Make sure as you do this that the posterior surface o the block remains square on the flat plate. Leave it undisturbed on the flat plate for the glue to cure (30-60 minutes).
Once the glue holding the blocks has dried, put index pins in the mould and mount the inside template to the anterior aspect of the mould. Scribe around the template at the corner and end blocks. (TMB will also use corner templates cut from the larger inside template - on one side - to make fine adjustments to the outline prior to carving the blocks.)
With the lines scribed on the blocks, excess wood can be removed from the end blocks, and the carving of the inside curves of the corner blocks can proceed. The end blocks are carved with a broad bladed chisel. Check with a square on the flat plate to insure that you are maintaining the correct angle. A flexible ruler can be laid across the outer curve of the block to visualize the transition from mould to block.
TMB makes the bottom block slightly convex to account for the tendency of the ribs to bow in secondary to chin rest tension. Additionally, Terry makes both the neck and bottom blocks tilted in slightly at the bottom (posterior ascpect) thereby increasing the length of the top of the instrument in relation to the back. The amount of tilt is something on the order of 1/2 mm.
The inside curves of the corner blocks - those which will support the C-bout rib - are carved with an in-canal gouge. As above, check with a square on the flat plate to maintain the correct angle. Use the scribe line only as a suggestion at this point, and realize that removing too much wood from the inside curve of the blocks at this point can drastically effect the angle of the corner once the ribs are glued in place.
I like to use graphite or carbon paper at this point between the edge of the square and the block to identify the high spots. This practice is frowned upon by the master.